Filament for electron gun



Se t. 20, 1966 D. SCIAKY FILAMENT FOR ELECTRON GUN 32 Sheets-Sheet 2 Filed July 31, 1964 United States Patent 6' 3,274,425 FILAMENT FOR ELECTRON GUN David Sciaky, Chicago, lll., assignor to Welding Research, Inc., Chicago, L, a corporation of Illinois Filed July 31, 1964, Ser. No. 386,725 7 Claims. (Cl. 313-237) The invention relates to an electron beam gun and has reference more particularly to a new and improved electron emitting filament for an electron gun which will be mechanically and electrically stable.

When devices of the character as described are used for welding, the stream of electrons is accelerated and focused by structure designed for the purpose whereby a high power density beam is produced for impinging on the work pieces, with the result that the energy of the beam is transferred to the work to cause fusion, The essential elements of such a welding device comprise a supporting body portion, a filament, a cathode, an anode and a focusing coil. The elements are so designed and have such correlation with each other that various metals and particularly those characterized by a high melting temperature can be satisfactorily welded within a vacuum.

An object of the present invention is to provide a filament for such an electron gun which will be inexpensive to produce, which will be highly efiicient in operation, and which will have a shape such as to materially facilitate asy insertion and removal of the filament from tie clamping means of the gun and which will emit a beam of electrons which is circular in cross-section.

Another object of the invention is to provide a filament which can be easily clamped in position so that it maintains the proper relationship to the anode so as to obtain reproducibility in perveance of the electron gun.

Other objects of the invention are to provide a new and improved filament for an electron gun that can be punched from a metal plate, thus making possible reproductions which will be accurate as to shape and dimensions; to provide filaments for an electron gun wherein the area for electron emission will be precisely the same for each filament; and to provide filaments for the purposes as stated which will be sturdy and mechanically and electrically stable.

Another object of the invention is to provide a filament for an electron gun which will be made of tantalum, or other material of low work function, which will be precisely shaped to provide a fiat unbroken emitting surface.

In electronbeam guns heretofore made, which utilized filaments of the direct heater type, the electron emitting surface was either oval, square or rectangular in shape. The beam formed from these emitters retained the shape of the emitting surface, and for this reason the welding results depended upon the orientation of the filament with respect to the direction of the welding. Other filament structures utilized thin, flat or round wires wound in a fiat spiral. The beam produced by filaments of,this type was non-uniform over the cross-sectional area of the beam because of the open areas in the emitting surface. In

order to lessen the magnetic field surrounding the filaments, bifilar structures were used when alternating current was used to heat the filament. These took the form of special bifilar spiral or folded-back non-inductive configurations. The filaments were found to be structurally weak, and would tend to distort easily and thus produce erratic results. The present structure overcomes these deficiencies in great measure and provides a filament structure which is easily made and mechanically rigid.

With these and various other objects in view, the inven tion may consist of certain novel features of construction and operation, as will be more fully described and particularly pointed out in the specification, drawings and claims appended thereto.

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In the drawings which illustrate an embodiment of the device and wherein like reference characters are used to designate like parts- FIGURE 1 is a longitudinal sectional view of a portion of an electron gun incorporating the improved filament of the invention;

. FIGURE 2 is an isometric view of the filament structure;

FIGURE 3 is a fragmentary sectional view which shows in detail the manner in which the filament can be releasably clamped to the current conducting electrodes of the gun;

FIGURE 4 is a plan view of a filament in clamped arrangement as shown in FIGURE 3;

FIGURE 5 is a schematic view showing electrical connections for the various elements of an electron beam gun as disclosed; and

FIGURE 6 is a detail view showingthe size and shape of the metal blank prior to the bending thereof for forming the filament.

Referring to the drawings, and in particular to FIGURE 1, the embodiment selected for illustrating the invention employs a cap or body portion 39 from which the various parts of the gun are suspended.

The current conducting electrodes 1 and 2 and the inner cage 3 comprise a unit which is supported from the insulating body portion. The electrodes 1 and 2 are spaced and insulated from each other and from the inner cage. The electrodes are thus mechanically connected to form a unit which includes a clamping arrangement for clamping the filament to the electrodes. Each electrode has a clamping bar, such as 4 and 5, disposed in contact with its outer surface, and each bar provides a lower flange 6 and 7 adapted to contact a shoulder such as 8 on its respective electrode. A clamping member 9 isprovided for each bar nad the same contacts its bar at iongitudinally spaced locations for which purpose each nember 9 is provided with feet 10. A bolt 11 extends through each of the members and through its associated clamping bar and has threaded connection with its respective electrode. The clamping members are preferably formed of metal such as copper and which has some resiliency since upon tightening the bolts 11 it will be understood that a spring loading action is applied to each clamping bar, thus forcing and securely maintaining the flanges 6 and 7 against a shoulder 8 to thus provide a good mechanical and elec trical clamp for the filament 12. The inner cage 3 of substantially cylindrical shape may be constructed of stainless steel and the cage is formed with a plurality of openings 13 whereby convenient access is provided for manipulating the screws 14. Release of the screws and disassembly of the clamping arrangement will be necessary in the event a filament has to be replaced.

The lower terminal end of the inside cage 3 is threaded as at 15 and this threaded end receives the retaining ring 16 for releasably retaining the cathode electrode 17 in place on the bottom of the cage. The said cathode electrode is maintained at a negative potential of approximately 50,000 volts and the same is provided with a center opening which receives the axially positioned filamcnt 12, The filament 12 is formed-from a strip of metal 18, FIGURE 6, such as tantalum, tungsten, or other suitable metal, the same having a shape as shown in FIGURE 6. The relatively wide extremities 19 comprise the portions of the same which are clamped between shoulders 8 and flanges 6 and 7 respectively. The connecting portions 20 narrow down the strip to a central section 21 which has a length, width, and shape whereby to permit the forming of a flat round emitting surface having flanges so as to obtain a cylindrical cap section. With the filament in clamped engagement with electrodes 1 and 2, as shown in FIGURE 3, the connecting portion 20 extends diagonal- 3 I ly downward and inward to the bend 22 whereupon the cylindrical section extends downward to the fiat circular emitting surface 21.

The formation of the filament 12, as described and shown in FIGURES 1, 3 and 4, results in a particularly rigid bridge-like and stable structure which is not atfected by a repeated cycling of heating and cooling or ion bombardment-the emitting surface always remaining substantially normal to. the mechanical axis of the electron gun.

The electron beam should emerge vertically from the gun and in this respect the filament is important. Its flat area provides an electron emitting surface of definite size and which can be maintained fiat or as an alternative the entire filament can be replaced at relatively little expense and in a most easy and rapid manner. Since the filament is accurately reproducible a change in filament does not interfere in any manner with the operation of the apparatus.

The shape of the filament is such as to locate the clamping portions in planes which are at right angles to the flat area.

For focusing and directing the electron beam so as to direct a beam of maximum density for welding the work piece, a focusing coil 23 is suspended by the screws 24 from the anode supporting ring 25. The said focusing coil essentially consists of a coil 26 encased in an enclosing shell 27 of iron. An air gap 28 exists between the interior cylinder of iron 29 and the iron cover plate 38. A relatively low voltage, direct current is caused to flow through the coil 26 to provide a magnetic effect within the central passage formed by the interior cylinder 29. The focusing coil is located below the anode where the electron beam starts to diverge. The action of the magnetic flux in the air gap is such as to cause the beam to converge and by adjusting the current flowing in the coils the beam of electrons can be caused to impinge on the work piece with maximum density for the most satisfactory welding operation.

Wherithe temperature of the filament 12 is increased to a predetermined extent, the kinetic energy of some of the electrons is also increased allowing them to escape from the filament. In a vacuum and under the influence of an electric field as produced by the cathode electrode 17 and the anode 30, the electrons are accelerated and they move in the direction of the field. Because the electron beam has a tendency to diverge, it is necessary to counter this natural phenomenon by providing the focusing coil 23. The coil is located a predetermined distance below the anode 30. v

The electrical circuit for the gun is shown schematically in FIGURE 5. The heating current for the filament is supplied by a high-current low-voltage D.-C. power supply 31. The rectifier is fed from the three-phase power supply lines L1, L2 and L3. The terminals 32 and 33 are connected to electrodes 1 and 2 and thus feed direct current to filament 12. The high voltage power supply furnishes a direct current at the desired voltage for maintaining the required electrical field between the cathode and the anode. The negative conductor 34 is connected to the conductor 32 and the conductor 35 completes the circuit to the cathode electrode 17. The positive conductor 36 from the high voltage power supply has connection with the anode'30 and a parallel circuit including conductor 37 is connected to the work-piece and grounded.

For more complete details of the electron gun, reference can be made to copending application in the name of David Sciaky, Serial 109,575, new Patent No. 3,187,216, filed May 12, 1961, and entitled, Electron Gun.

It is to be understood that the invention is not to be limited to or by details of construction of the particular embodiment thereof illustrated by the drawings, .2 5 various other forms of the device will, of course, be ap uarent to those skilledin the art without departing from the spirit of the invention or the scope of the claims.

What is claimed is:

1. An electron emitting element comprising a strip of metal having a shape which provides a pair of spaced clamping portions and a central cylindrical section connecting with the clamping portions.

2. An electron emitting element comprising a strip of metal having a shape which provides a pairot spaced clamping portions and a central cylindrical section connecting with the clamping portions, said portions and the end of cylinder being disposed in planes approximately at right angles to eachother.

3. An electron emitting element comprising a strip of metal having a shape which provides a pair of spaced clamping portions and a. central cylindrical section condiagonal portions connecting the clamping portions with the cylinder, said clamping portions and the end of the cylinder being disposed in planes approximately at right angles to each other.

4. An electron emitting element as defined by claims 1 and 2, wherein the metal strip consists of tantalum.

5. An electron emitting element as defined by claims 1 and 2, wherein the cylinder at diametrically opposite sides is joined to the diagonal connecting portions by the metal of the strip.

6. An electron emitting element comprising a strip of metal of substantially the same thickness throughout but which varies in width, said element having a shape providing a pair of spaced clamping portions, a centrally located cylinder and diagonal portions connecting the clamping portions with the cylinder having a flat area at its end, said clamping portions being disposed in parallel planes and which having a right angler-elation with the flat area, and the said strip having its maximum width at the clamping portions.

7. An electron emitting element comprising a strip of metal of substantially the same thickness throughout but which varies in width, said element having a shape providing a pair of spaced clamping portions, a centrally located circular flat area and diagonal portions connecting the clamping portions with the flat area, said clamping portions being disposed in parallel planes and which have a right angle relation with the flat area, the said strip having its maximum width at the clamping portions and progressively diminishing width along the diagonal portions.

No references cited.

JOHN w. HUCKERT, Primary Examiner.

A. I. JAMES, Assistant Examiner. 

1. AN ELECTRON EMITTING ELEMENT COMPRISING A STRIP OF METAL HAVING A SHAPE WHICH PROVIDES A PAIR OF SPACED CLAMPING PORTIONS AND A CENTRAL CYLINDRICAL SECTION CONNECTING WITH THE CLAMPING PORTIONS. 